Preheat the oven to 425°F. Line a baking sheet with parchment paper.
Whisk flour, sugar, baking powder, and salt together in a bowl.
Cut butter into flour mixture using a pastry blender or two knives until butter is the size of peas (don't overwork it... bigger pieces make a flakier biscuit). Add chopped chocolate and mix lightly. Stir cream and yogurt together in a second bowl, add it to the flour mixture, and blend with a fork just until dough comes together (I actually use a rubber scraper instead). Don't overmix!! Pat out dough onto a lightly flour surface into a circle about 1-inch thick. Using a 2 1/2-ish inch round cutter, cut out as many shortcakes as possible and place on prepared baking sheet. Gently press scraps into a 1-inch thick circle and cut out remaining biscuits (you should have six. I had six and a mini one).
Brush with heavy cream and sprinkle lightly with turbinado sugar (regular sugar is also fine). Bake until golden, about 15 minutes.
Crush 1 cup of strawberries in a bowl with a potato masher. Stir in fresh berries, sugar, and lemon juice. Let stand for at least 30 minutes or up to overnight.
Beat cream, powdered sugar, and vanilla together in a bowl with a mixer on high until soft peaks form.
Bring cream and corn syrup to a simmer in a small saucepan over medium heat until steamy but not boiling. Place chopped chocolate in a heatproof bowl and pour warm cream mixture over top. Let stand briefly to melt, then whisk until smooth. (This sauce is also good on ice cream).
Halve the shortcakes horizontally. Place bottoms on serving dishes, cut side up, then top with strawberries, whipped cream, optional chocolate sauce, and remaining shortcake halves.